New Insights into the Cleaning of Paintings

18 • smithsonian contributions to museum conservation
Italian Conservation Schools was published, La Chimica del
Restauro (Matteini and Moles, 1989). It is a very useful tool
that discusses many materials used in the creation of artifacts,
together with the materials commonly used during conservation
treatments. Among these, cleaning materials are presented from
a chemical and physical point of view; the way they work is explained,
and the issue of their toxicity is also discussed. At the
time of its first publication, this book systemized the knowledge
and the practice of restoration, including cleaning. However, the
Teas triangle diagram of solvents was only briefly mentioned and
was still represented in an imprecise way.
THE STATE OF THE ART
In the second half of the twentieth century, the cleaning of
easel paintings and polychrome objects in Italy was mainly performed
with neutral organic solvents and acid and alkaline reactants,
sometimes mixed together and/or with water. One of the
most commonly used mixtures was obtained by mixing water
with an alkaline substance in variable proportions.
The practice of cleaning was mainly based on a set of formulas
and recipes considered effective to solve some problems such as
removal of varnishes and retouchings; everything was entrusted to
the practical skills of the restorer and his or her experience. Testing
was performed with mixtures of different solvents that were ready
in the studio for use and were considered efficient enough to remove
ingrained surface dust rather than varnishes, unknown coatings
on paintings, old retouchings, and old fillings. As reported in
Table 1, each of those mixtures usually had an acronym as a name,
made up of a number (the number of substances in the mixture)
and letters (referring to the first letter of each substance).
This was obviously the common practice in private studios,
whereas museums and studios belonging to the Soprintendenze
could usually afford a good preliminary diagnostic campaign, which
made it possible to avoid such empirical approaches. The Opificio
delle Pietre Dure in Florence was the first institution to try and use a
carrier or supporting material called a stearic emulsion, commonly
known as pappina fiorentina (Matteini and Moles, 1984). This allowed
a suspension of organic solvents and alkaline substances to
be prepared in a very dense paste, thus avoiding their diffusion into
the paint layers, and it proved to be much more efficient than the
traditional methods relying on paper or cotton substrates.
Sometimes cellulose ethers were also employed as supporting
materials for solvents. This was a common practice in cleaning
frescos and stone artifacts, where a buffer mixture including
a detergent and ethylendiaminetetraacetic acid (EDTA) in water,
known as AB57, used carboxymethyl cellulose as the supporting
material (Mora and Philippot, 1977; Colalucci, 1990).
Solvents with a high or medium level of toxicity were commonly
used, e.g., butyl ammine, pyridine, carbon tetrachloride,
and formic acid. It was also common practice to wash cleaned
areas of the painting with liquid or gelled solvents. This operation
was inappropriately called neutralization and was performed in
order to eliminate any residue of the solvent or the acidic or
alkaline substance previously employed during the cleaning process
in order to halt its reaction. In practice, this practice only
interfered with those solvents’ evaporation time.
On the positive side, some very old methods, such as burning
or regeneration of old varnishes, had gradually been abandoned.
These methods were also quite risky for the health and
safety of the restorer.
EARLY DEVELOPMENTS
The papers from the Brussels IIC Congress of 1990 (Mills
and Smith, 1990) and other literature focusing on more updated
Table 1. Some common mixtures employed in restoration. Note that the acronyms stem from the Italian name of the solvents. DMF =
dimethylformamide; n/a = not applicable.
Mixtures Components ratio
2 A water + ammonia 1:1
3 A water + acetone + ethanol 1:1:1
4 A water + ammonia + ethanol + acetone 1:1:1:1
AB water + butylamine 1:1
ABD water + butylamine + DMF 1:1:1
Benzine 80°C–100°C Hydrocarbons n/a
Nitro thinner mixture of esters, ketones, alcohols, and aromatic hydrocarbons variable, depending on the producer
DA DMF + amyl acetate 1:1
DAN DMF + amyl acetate + nitro thinner 1:1:1
DIDAX DMF + synthetic thinner + xylol + acetone (35 + 15 + 10 + 10 mL, respectively) 3.5:1.5:1:1
Petroleum ether Hydrocarbons n/a
White spirit Hydrocarbons n/a